Pneumatic impact device



June 218, 1949-- O. c. DREssER ErAL 2,474,235

PNEUMATIC IMPACT DEVICE Filled Dec. 14, 1945 5 Sheets-Sheet 1 1&2

Th1/vc nhw OSCAR CA DRESSER OSCAR NORGORDEN CARROLL R. SHULER FRANCIS J.SHANAHAN v June 28, 1949. o. c. DREssER ETAL 2,474,235

PNEUMATIC IMPACT DEVICE Filed Dec. '14, 1945 5 Sheets-Sheet 2 l l x o I:,I L 2 21;, I fg -I 2 l g,

l I I gwue/rvtou' m oscAR c. oREssER a N oscAR NoRGoRDEN FRANCIS J.SHANAHAN CARROLL R SHULER www,

June 28, 1949. o. c; DREssER ETAL immuno mPAcT DEVICE Filed Dec. 14.1945 5 Sheets-Sheet 3 s o 008-6 o o O C) O G I, Q lo ILE- 4i I @WUR/whoaos'cAR c. oREssER oscAR NoRsoRoEN FRANCIS J. SHANAHAN CARROLL R. sHuLERJune 28,1949. QQ c. DRESSER ml. 2,474,235

INEUMATIC IMPACT DEVICE I Filed nec. 14. 1945 5 sheets-sheet 4 Swan/MouOSCAR C. DRESSER OSCAR NORGORDEN FRANCIS J. SHANAHAN CARROLL R. SHULERamada@ 1949 PN EIMATIC MPACT DEVICE Oscar C. Dresser, Arlington, Va.,Oscar Norgorden,

gton, D. C., and

Francis J. Shanahan,

Alexandria, and Carroll R. Shuler, Stanley, Va. Application December 14,1945, ser-laine. 635,118'

' 7 claims. (ci. 121-21) (Granted under the actv of March amended April30, 1928; 370 0.

This invention relates to pneumatic impact devices and more particularlyto pneumatic impact devices for shock testing apparatus and methods Y ofcontrolling the impact devices.

Where apparatus is to be subjected in use to severe shocks, as forexample vwhere apparatus is to be mounted on ship board and subjected toconcussion and shock due tov firing of the ships guns as well as toVshocks resulting from enemy action, it becomes necessary to sodesignthe apparatus and the mounting for the apparatus that the apparatus willwithstand these shocks. For this reason impact or shock testing machineshave been developed whereby the apparatus may be subjected to shocks orimpacts simulating that vwhich will be encountered in actual use. Whileimpact devices have been heretofore available, in general these deviceshave included no means for controlling the duration of the shock appliedto the apparatus being tested and have been capable of delivering only avery short duration shock. 'I'hus Where large articles or articleshaving a considerable height are subjected to shocks, the force of theshock is largely absorbed in the lower portions of the article and nosubstantial force reaches the upper portions. By increasing the durationof the shock, however, it is possible to cause the force to be appliedmore uniformly over the article being tested. Furthermore, it has beenfound that the more common types of shocks encountered in practice areof relatively long duration and hence unless the impact-device iscapable of delivering a similar type of shock, the value of the impacttest becomes very questionable.

Another import-ant consideration in impact or f shock testing is thatbut one blow be delivered and that secondary shocks be eliminated orreduced. to such a magnitude that they are unimportant. Where the forcesinvolved are very large the elimination of secondary shocks resultingfrom recoil and rebound is extremely difiicult. Failure to eliminatesecondary shocks, however, results in an impact test of unknown or atbest difficult to estimate characteristics.

An object of this invention is to provide a new and improved pneumaticimpact device.

A further object of this invention is to provide a pneumatic impactdevice which will not produce secondary shocks.

' A further object of the present invention is to provide a pneumaticimpact device whereby the acceleration, duration, and velocity of theshock may be accurately controlled, and a method of controlling thesefactors.

piston.

3, 1883, as G. 757) In accordance with one embodiment of this inention,a pneumatic impact device may be provided comprising a large cylinderhaving mounted in the forward end thereof a striker shaft xed to apiston, slidably journalled in the cylinder. A second piston is alsoJournalled in the cylinder and spaced from the rst piston. Means areprovided for controlling the gas pressure between the two pistons tocontrol the duration and acceleration of impact and means are ,providedfor applying air pressure to the second piston while retaining thesecond piston in cocked` position. Means are also provided forreleasing`. the second piston to cause the first piston to move thestriker shaft forward with great force. Means are also provided forpreventing secondary shocks resulting from rebound of the second Otherobjects and advantages of the present invention will be apparent fromthe following detailed description taken in conjunction with thedrawings wherein:

Fig. 1 is a plan view of a. pneumatic impact device constructed inaccordance with one embodiment of this invention;

Fig. 2V is a sectional view taken substantially along the line 2 2 ofFig. 3 is a detail, the line 3 3 of Fig. 2;

Fig. 4 is a section taken along the line 4 4 of Fig. 2;

Fig. 5 is a fragmentary, detail view of the upper end of the pushrodlatching mechanism;

Fig. 6 is a diagrammatic representation of this impact device;

Fig..1; sectional view taken along Fig. 7 is a fragmentary section takensubstantially along the line 1 7 of Fig. 2; and

Fig. 8 is a section taken along the line 8 3 of Fig. 7.

Impact or shock testing apparatus usually comprises two elements: amovable platform on which the apparatus to be tested is supported and towhich it is secured, and an impact device for delivering a blow to theplatform'whereby a shock will be applied to the apparatus. The presentinvention is directed solely to the impact device and is intended foruse with any suitable apparatus support.

Referring now to the drawings, and particularly to Figs. 1 and 2thereof, it will be seen that this device includes a base plate lll onwhich is rigidly mounted a large cylinder Il. An exhaust chamber I2 ismounted on the upper side of the cylinder and is connected thereto bylongitudinally extending slots l 3 formed through the upper sidecf thecylinder at the base of the exhaust chamber.

Slidably mounted in the left portion of the cylinder ii is a heavypiston I4, the periphery of which closely engages the interior wall ofthe cylinder il and is provided-with a number of piston rings I8 fittedinto annular grooves i6, formed in the periphery of the piston. A shortstriker shaft Il is mounted on the left face of the piston it,substantially in the center thereof. and extends slldably through asuitably apertured end plate I8, rigidly iixed to the left end of thecylinder Ii. In practice, it has been found desirable to form the shaftI1 integrally with the piston Iii; however, this is not necessary ifsuitable means be employed for securing the shaft to the piston I6. Theleft end of the piston .shaft il is provided with a striker plate 2iformed of a material which will resist deformation resulting fromimpact, such as manganese steel. in order to prevent the piston I4 frombeing with- :irawn too far into the cylinder II, a retaining :ollar orflange 22 is mounted in an annular groove 23 formed in the periphery ofthe shaft I1 and spaced slightly from the left end thereof, ;he collar22 being so located as to bear against a. shoulder portion 2d,integrally formed with left side of the end plate IB of the cylinder II,when he piston I6 is moved to its extreme right posi- Lion.

Slidably mounted within the cylinder II and ,zpaced from the right sideof the piston I4 is a aecond piston 28 of similar dimensions to theoiston I4 and provided with annular peripheral grooves 28 in which aredisposed piston rings 30. 'I'he rear piston 28 is provided with a long,heavy shaft 3| which extends to the right, as viewed in Fig. 2, throughan end plate 32 rigidly mounted on the right end of the cylinder II, thepiston shaft being slidably journalled in a stuffing box 33 mounted inthe end plate 32 to prevent leakage of air during movement of the shaft3i. A retaining sleeve 34 is associated with the stufiing box 33 and isadjustable to compress the stuffing to obtain the desired tightness oft.

Since it is impractical to make the shaft SI integrally with the piston28, because of the considerable length of the shaft the shaft 3| extendsthrough the center portion of the piston 28 and is provided with aflanged end portion 35 at its left end which seats in a iiared portion36 of an aperture 31 formed through the piston 28. A heavy sleeve-shapednut 38 is threaded on the portion of the shaft 3l extending to the rightfrom the right side of the piston 28 and is adjusted to' rigidly securethe shaft 3| to the piston. A locking pin 39 is associated with the nut38, as is well known in the art, to prevent loosening of the nut.

By flaring the left end of the shaft 3l, the mass per unit area of theexposed end of the shaft is made substantially equal to the mass perunit area of the remainder of the left side of the piston 28 and thus,since the eiect of the pressure in the space between the pistons will beexerted on the piston 28 and the shaft 3l proportionally to theirrelative areas, a substantial reduction is made possible in the amountof the thrust that must be carried by the nut 38 during acceleration ofthe piston and shaft. At the same time, the shaft is rigidly secured tothe piston so that there is no possibility of the shaft being separatedfrom the piston during forward movement of the piston; because of thevery large forces involved in the operation of this apparatus, this isan i-mportant consideration. I

While by reason of the design of this apparatus, the force or momentumpresent as the piston 28 and shaft 3i rebound or recoil after an impacthas been delivered is largely absorbed or expended in forcing the airtrapped behind this piston 28 in the charging chamber out of the exhaustchamber, in some cases due to variations in the load on the platform orto variations in the charging pressure or other conditions, some forcemay not be absorbed, and the piston may move rearwardly withconsiderable momentum. Since the exhaust slots or ports i8 are locatedsubstantially in the mid-portion of the cylinder Il, the portion of thecylinder to the right of the ports has no outlet and may be employed aspressure chamber. Thus, if the piston 28 recoils past the ports i3, theair in this pressure chamber is compressed thereby and the momentumthereof largely absorbed. In order to prevent damage to the stulng boxassembly 33 in the event that the exhaust chamber is not opened or otherfailure 3l, the left end of occurs, a sleeve 83 is mounted inside theright end of the cylinder il and is provided with a heavy rim lid at itsleft end which serves as a seat against which the piston 28 may strike.Ordinarily, however, the piston will not recoil sufficiently to cause itto strike.

The starting position of the pistons I4 and 28 is shown in Fig` 2. Inthis position the piston I4 is retracted to the right so that the collar22 seats against the shoulder 24 formed on the left side of the endplate I8, while the piston 28 is positioned so that its right edge isimmediately to the left of the ports I3 formed in the upper side of thecylinder II and communicating with the exhaust chamber I2. The piston 28is initially locked in this position by a locking mechanism located tothe right of the end plate 32 and arranged so as to be engageable withthe shaft 3|, the locking mechanism being shown in Figs. 2, 3, '1, and8. As shown in these drawings, a heavy, flat bar 48 is mountedtransversely through the shaft 3i at a point suitably spaced from theright end thereof, the outer ends of the bar projecting a substantialdistance from either side of the shaft. In locked position the leftsides, as viewed in Figs. 7 and 8, of the outwardly projecting por-'tions of the bar 48 bear against a pair of heavy, spaced rollers 49located on either side of the shaft 3| and rotatably mounted on a pairof spaced, axially aligned shafts 50 journalled in the left end portionof a suitably formed, pivotally supported, latching block 5I, therollers 48 being i so disposed with respect to the bar 48 that the axisof the rollers lies in a plane with the midpoint of the left faces ofthe bar 48 when in locking relation, thus providing a condition ofsubstantial equilibrium wherein slight restraint is required to maintainthe block 5I in locking relation, that is, to prevent the block 5I frompivoting upward prematurely. Rotation of the shaft during longitudinalmovement thereof is prevented and alignment of the bar 48 with therollers 43 is maintained by a pair of spaced, parallel guide rails 41which are mounted on the opposed, inner sides of a pair of spaced,parallel, upright plates or walls 53, rigidly nxed to the base I0 of theapparatus. The rails 41 extend to the right from a point slightly spacedto the left of the rollers 49, when the rollers are in locking position,a suilcient distance so that at all times the undersides of the bar 48bear against the upper surfaces of the rails.

. being suitably journalled in the As may be seen in Fig. 3, the blockcams El are pivoted l a crankarm S3 xed stub shaftsri, block andexacuasc Y at its right f tend a short distance from either side of theblock, the outwardly extending portions thereof 5l has formed along thecenter of the underside thereof a semicylindrical recess 54 whichextends the length thereof and which, when the block is pivoteddownwardly to bring the rollers tion, receives the upper portion of theshaft 3|, thus permitting the rollers to be aligned as hereinbeforedescribed with the bar I8. To expose the rightpol'tions of the rollersso they may bear against the bar I8, as shown in Fig. 8, the block 5i isprovided with a transversely extending recess 55 in its lower side ofsumcient depth and lower portions of the block, as shown in Figs. 3 and8,130 accommodate the rollers.

Because of the substantial when the rollers 68, it is relatively simpleto this position and little restraint is required. While it is desiredto prevent forward movement of the shaft 3i, the block 5| is preventedfrom the upright walls 53,. the shaft being disposed beneath and atrightl angles to the path of reciprocation of the shaft 3|. -The upperportions of the cam plates are formed to provide arcuate cam surfaces59, which, when the rollers are in locking position, bearagainst theundersides of lugs 13, which may be integrally formed with either sideof the block 5I and extend outwardly therefrom a short distance.Referring to Figs.

upright walls 53.

into locking posiwidth both to expose the rollers and also to reof anaperture'll 2 and 3, it will be seen that the upper Vportion of each ofthe cam plates 51 has integrally formed with the right end thereof ashoulder 5I and that the shoulder is provided with an undercut recess ornotch 62 of suitable size to receive the lug 60, the lower surface ofthe recess being in a plane' with the arcuate cam surface of the camplate.

When the cam plates are pivoted in a counterr in Fig. 2, the lugsclockwise direction, as viewed 53 enter' the recesses 62 and accidentalupward pivotal movement of the block 5i is eectively prevented.

When it is desired to release the shaft 3i, the in a clockwise directionby distance beyond the left, upright wall 53. VReferring again to Fig.2, it will be seen that an actuating device, such as the piston assembly64, is connected to the outer end of the crankarm 63 by alink bar 55 sothat when the piston 64 moves upwardly, the cam plates will be pivotedin a clockwise direction and conversely when the piston movesdownwardly, the cam plates will be pivoted in a counterclockwisedirection, locking the block 5i in position. When the cam plates aremoved in a clockwise direction releasing the shaft 3i, initially thelugs' are disengaged, the recessed shoulders 6l moving to relativelythereto, and then the arcuate cam surfaces 59 bearing against theundersides of the lugs 50 push the lugs and block 5i slightly uptheright Y 6 tial equilibrium theretofore present and since at urging thepiston 2l and shaft 3i forward are very'great, by reason of the cammingaction of the bar Il bearing now against the lower portions of therollers 45, the block 5i will be deflected upwardly with great force. Inorder to prevent damage to the apparatus from this sudden, upward thrustof the block 5|, a, shock absorber 66 is provided and is pivotallymounted on spaced brackets 6l, which are in turn fixed to the uppersides of the upright walls 53. The shock absorber' piston shaft 68 ispivtally connected to the forward end of the block 5|. The shockabsorber while permitting the block 5i to be pivoted upwardly, preventsthe block from being pivoted beyond a suitable point and also absorbsthe thrust resulting from the camming action of the bar 48 and rollers49. In prep'aring'this impact device to deliver an impact or shock, theexhaust chamber i2 is closed by a poppet valve 10 which seats in theleft end formed through the right side of the exhaust chamber I 2, asmay be seen in Fig. 2. The poppet valve is provided with a long valvestem 72 which extends to the right therefrom through a small housing 73,provided with into a cylinder 'l5 iixed to the may be seated, thusclosing the exhaust chamber,

or by admitting air under pressure to the port 18, the poppet valve willbe moved to the left, thus opening the exhaust chamber.

Port Tl, which is'formed adjacent the left end of the cylinder 15, isselected to have such a size with respect to the size of the chamberprovided inthe cylinder l5 between the left end wall and the piston itthat when the piston 76 starts to move to the left in the operation ofthe apparatus, the air in this chamber will be compressed somewhat andthen will escape at a controlled rate through the port TF, thusabsorbing the kinetic energy of the moving piston 'i6 and substantiallypreventing rebound thereof which would tend to seat the poppet valve andclose the exhaust chamber. 1n order to prevent any eifective closing ofthe exhaust chamber such as might result from slight rebound, thedisplacement of the poppet valve resulting from the movement of thepiston 'it to the left is made to be substantially greater than thedistance required to open the exhaust chamber outlet; thus, any slightrecoil of the piston 76 is rendered insuiiicient to aifect the effectiveopening of the exhaust chamber.

The cylinder 'l5 is made to have an internal diameter slightly less thanthe effective diameter of the poppet valve aperture 1| and thus when thepressure in the exhaust chamber is equal to the pressure in the rightportion of the cylinder l5, tendingV to force the poppet valve to theleft and to open the exhaust chamber, because of the difference in thestatic forces acting respectively on the poppet valve and on the pistoni6, the4 being then equivalent to the dli'ierencf,l between the staticforce acting on the static force acting on the piston 18.

In the operation of this apparatus, after the piston shaft 3I has beenreleased and the piston 28 has begun to move to the left under the forceof the air pressure in the charging chamber, that is the portion of thecylinder II to the right of the piston 28, the pressure in the chargingchamber and exhaust chamber will drop due to the adiabatic expansion ofthe air. Where the pressure on the right side of the piston 18 has beenadjusted to be equal to the charging pressure, which is the desiredoperating condition, this drop in pressure will cause the poppet valveto tend to open. Early opening of the poppet valve obviously wouldrelease the charging pressure prior to the completion of the thrust ofthe piston 28. Thus, in order to prevent premature opening of the poppetvalve 1li, a latchlng mechanism is provided and is associated with theright portion of the poppet valve assembly, as shown in Figs. 2, 4, and5. The right portion of the poppet valve stem 12, that is the portionthereof extending from the right side of the piston 16 through the rightend wall of the cylinder 15,v is made quite long and is journalledthrough the upper portion of a vertically disposed, supporting plate 82,the plate 82 being rigidly mounted on the end wall 32 of the cylinderII. The right end of the stem 12 extends substantially beyond the rightedge of the plate 82, as may be seen in Fig. 2. A vertically movablepushrod 83 is slidably iournalled in two vertically spaced shoulders 84and 85 integrally formed With the right edge of the plate 82 at theupper and lower ends thereof. These shoulders are suitably recessed toreceive the pushrod and to serve as guides therefor, the pushrod beingheld in position therein by a retaining plate 86 xed to the lowershoulder and a pair of vertically spaced, retaining plates 81 fixed tothe upper shoulder, the upper retaining plates being spaced to permitthe outer end of the stem 12 to extend therebetween. A roller 90 which,serves as a cam follower, is mounted at the lower end of the pushrod ona short shaft 8l the poppet valve and suitably journalled in the lowerend of the push rod 83 and the roller 9B bears on the upper surface ofthe piston shaft 3l. The upper portion of the push rod 83 is providedwith a semi-cylindrical aperture 83 of slightly greater diameter thanthe valve stem 12, which extends therethrough and the base of theaperture 83 opens into a larger aperture 94 formed immediatelytherebeneath. A pair of key rails 95 are mounted on either side of thevalve stem 12 at the right end thereof and are so located with respectto the push rod 83 that when the push rod is in its lower position, theleft ends of the rails 85 bear against the right face of the push rod,the upper portion of the valve stem 12 being then disposed in thesenil-cylindrical aperture 98 formed in the upper portion of the pushrod. By suitably spacing the retaining plates 81 mounted on the Push rodsupporting bar 84, the outer portions of their opposed edges will`engage the upper and lower sides of the key rails 85 and preventrotation of the valve stem, thus maintaining the proper alignment of thekey rails with respect to the apertures 93 and 94 formed in the push rod83.

It will be apparent that in order to permit the poppet valve 10 to moveto the left to open the' exhaust chamber I2, it is necessary that thepush rod 83 move upward a sufiicient distance so that the valve stem 12and associated key rails SI may move through the larger aperture 94formed immediately beneath the semi-cylindrical aperture 93 in the pushrod 83. In order to move the push rod 83 in timed relation to themovement o? the piston 28, the upperv surface of -the piston shaft 3iimmediately beneath the roller t@ is indented slightly to form aninclined cam surface 86, the lower portion of the cam surface s@ beingso located on the piston shaft BI that when the piston 28 is in itsstarting position, the roller @d at the lower end of the push rod 63,bears against the lower-most portion of the cam surface. 'Then as theshaft 3i is moved to the left, the inclination of the cam surface 9Sbeing upward to the right, the push rod 83 is cammed upward, releasingthe valve stem 12 and permitting the valve 10 to open the exhaustchamber I2.

At the start of a cycle of operation of this pneumatic impact device,the exhaust chamber I2 is closed by admitting air through the port 11 tothe left side of the piston 16 disposed in the poppet valve cylinder 15,thus moving the poppet valve 10 into the closed position. The push rod83 then moves downwardly, being urged downwardly by a flat spring |02mounted on the upper side of the bar 84 and bearing against the upperend of the push rod 8S. This locks the valve stem 12 in its extremeright position. Either prior thereto, or at the same time, air may beadmitted through a port m0, located to the left of piston I4 in thelower side of the cylinder il, to force thepiston I4 to the right, untilthe collar 22 seats against the shoulder 24 formed on the end plate I8.It will be understood that any other suitable means may be employed forretracting the striker piston I4. Since in practice it is desirable thatthe striker plate 2| be in direct contact with the platform to which theshock is t0 be delivered, the striker piston may be moved to startingposition by moving the platform as required. At the same 'time air isadmitted through a port IOI opening into the cylinder Il between thepistons I4 and 28, the port IUI being located at a point adjacent theright side o! the piston I4 when the piston I4 is in its extreme rightposition, and the piston 28 ls moved to the right to starting position.

When the piston 28 is moved to the right to starting position, theweight, of the piston shaft latching mechanism causes the rollers 48 tobe moved downwardly into locking position by the pivoting action of theblock 5I. The cam plates 51 are then plvoted in a. counter clockwisedirection to cause the recessed shoulder 6I to engage the lugs 60 formedon either side of the block Il in latchlng position. Air is thenadmitted through the main charging port |04 to the charging chamber ofthe cylinder II to obtain the required pressure. After the air in thecharging chamber is at the required pressure, the exhaust valve 18 ispreloaded by bleeding the front end of the exhaust valve cylinder toatmospheric pres. sure and air at the charging pressure is admitted tothe rear end of the exhaust valve cylinder through the port 18. Asstated hereinbefore. the diameter of the valve piston 16 is made lessthan the diameter of the poppet valve 10 so that in the preloadedcondition described, the resultant static forces will be suilicient onlyto maintain a tight seal. Where atmospheric pressure is to be usedbetween the pistons I4 and 28, the piessure is then adjustedtherebetween as required and at the same timeis similarly adjusted onthe left side of the piston I4. If greater than atmosp heric pressure isto be used between the pistons.

pressure is applied through the port IOI closed by plug i| and alsothrough port |00 closed by plug III to the space between the frontpiston and the end plate I8, the latter being necessary to maintain theposition of the front piston until the rear piston is released. If lessthan atmospheric pressure is desired in the space between the pistons,the air therein is exhausted through an exhaust port I closed by plugII2, and adjacent the inlet port IOI to obtain the required degree fvacuum. In this case the position of the front piston is maintained bythe collar 22 on the shaft I 1.

air at the required After obtaining the required absolute pressure inthe space between the pistons, firing is accomplished by energizing thepiston assembly 64 to rotate the cam plates 5'i in aclockwise'direction, as hereinbefore described. When the rear piston 28is released, it is driven forward by the expansion of the air in thecharging chamber and compresses the air between the pistons. As thepressure in the charging chamber decreases due to expansion, theresultant force on the exhaust valve will change in direction and willtend to open the valve because of the ynear balance theretoforeestablished. However, the valve is temporarily held closed lby thelatching mechanism 83. The loss of the sealing force resulting from thepressure in the exhaust chamber dropping causes a slight unseating ofthe poppet valve; by holding the dimensional tolerances of the latchingassembly 83 within close limits, it has been found in practice that theloss is insignificant. Compression of the air between the pistons I4 and28 causes the piston it to move forward and causes the striker plate 2lto deliver an impact, the air between the piston i8 and the end wal! i8being released through venting apertures 108, formed in the shaft Il,having their left ends so located that when the piston i4 is in itsextreme right position they are effectively closed by the plate i8, asmay be seen in Fig. 2,' but so located that as the piston I4 begins tomove forward, the endsare moved beyond the wall I8 and exposed toatmospheric pressure. The venting apertures i016 communicate with acentrally disposed aperture G07 in the shaft i7 which connects at itsright end with a number of radially extending venting apertures 408, theouter ends of which extend to the left surface of the piston i6. Thusprior to ar.; considerable pressure developing in the chamber formedbetween the end plate i8 and the piston I8, the forward movement of theshaft il exposes the ends of the venting apertures I 06 and permits vthe air to escape.

As the piston 28 moves forward, the cam rolle/rA 80 following the camsurface 98 raises the push rod 83 and releases the valve stem l2. Thepoppet valve is then free to move to the left to open the exhaustchamber. Since the pressure on the right side of the piston i8 in thechamber l5 is maintained at the original charging pressure, as thepressure in the charging chamber and exhaust chamber drops due to theadiabatic expansion of the air therein, the pressure on the right sideof the piston 16 will tend to open the exhaust chamber. The opening ofthe exhaust chamber poppet valve is timed to occur just prior to thepiston 28 reaching its maximum forward thrust so that as the piston 28begins to recoil, the exhaust chamber exit will be fully open permittingescape of the air in the charging chamber through the ports 14.

By reason of the design of the present appara- `pheric, the pressure Psahead of tus the duration of the impact or shock, the peak acceleration,and the iinal'velocity may be predetermined. These factors are,inter-related and in any given case of the values desired for any twoofthese factors determinesthe value of the third factor.

The essential parts of the impact device that must be considered in atheoretical analysis are shown in Fig. 6. It will be noted that thevarious control mechanisms and construction details which are needed inthe actual equipment have been omitted and that a platform |08 on whichthe equipment under test is mounted is shown, the forward end of theshaft I1 of the forward piston I4 being in contact with the edge of theplatform. The mass of the piston ldand of the platform and equipmentlocated thereon may be I considered as a unit and represented by thesymbol M. If the pressure P11Y between the two pistons is atmospheric orgreater than atmospiston is, as hereinbefore stated, made equal to P2.Thus the pressure Pz between the two systems will not push 'the pistonI4 and the platform away from its normal, or firing position previous tothe initiation of the shock cycle. The pressure P1 in the chargingchamber piston 28 is, of course, much greater than the pressure P2previous to firing.

At the moment that the latching mechanism holding the piston 28 isreleased, the initial force (F1) acting on the piston 28 and urging itto the left, is equal to the pressure in the charging chamber (P1) timesthe exposed area on the rear surface of piston 28'less the pressurebetween the piston (Pz), multiplied by the area of piston I8 on the sidebetween the two pistons, and may be represented by the equation F1=P1A2a-P2 A14, wherein F1 equals the force acting on piston 28, A21:y thearea on the rear surface of piston 28 and A14 the area of piston i0.

As the piston v28 moves forward, the pressure R: between the pistonsincreases rapidly and the tends to move piston i4 and the platformforward. Since the mass M in a practical case is many times the mass ofthe piston 28 and shaft Si, the gas between the pistons will becompressed to apressure correspondingly exceeding the initial pressurein the charging chamber. The piston 28 comes to rest when the energyexpended by the expansion of the gas inthe charging chamber is equal tothesum of the work done on the gas between the two pistons and the workdone on the piston i0 and the platform; that is, when the workdone bythe adiabatic expansion of the gas in the charging chamber has causedthe pistons i8 and 28 to attain the lsame velocity, the pressure betweenthe two pistons will have reached a maximum: thereafter, the piston 28recoils. Since, in a practical case, 'the mass of piston I8 and theplatform' greatly exceeds the mass of piston 28, the pressure P2ibetween the pistons when the pistons are moving at the same velocitywill exceed the initial pressure in the charging chamber P1 by manytimes and thus, for the short time interval during which the pressurebetween the pistons is many times the initial pressure in the chargingchamber, a large force (shock) is exerted upon the piston i4 andplatform I08, and, at the same instant, an equal and opposite force isexerted upon the piston 28. Piston 28 is thus decelerated and then,reversing direction, accelerated rapidly by of course, a selection theforward to the. rear of a lower gamma value `mum temperature can theforce exerted on piston 28 by the gas between the pistons.

The magnitude and the duration of the shook and the minimum spacingbetween the piston are a function of the initial pressure between thepistons and the gamma value of the ses between the pistons. Thus it ispossible to increase the range through which the magnitude and dura tionof the shock can be varied by using g with dierent gamma values fromthat of air for the gas between the two pistons. For example, while airhas a gamma value of 1.4, argon having a gamma value of 1.6, which ishigher than 'that of air, may be employed and will enable a, longerduration shock, that is, a shock having a lower peak acceleration. to beobtained with the same minimum spacing between the two pistons at themoment of recoil of the piston 2d.

It will be apparent that sumcient pressure and volume must be maintainedin the space between the pistons to prevent the piston 28 from f 1 ffthe piston Id. By employing a gas having a low value, a greater pressuremay be developed between the pistons than 'would be the case with a gasof higher gamma value and yet 'the minimum spacing between the pistonsbe unailected. Ordinarily, of course, an increase in nal pressure forany given initial pressure is achieved only by increasing thecompression oi the gas between the pistons and thus decreasing theminimum spacing. Thus with all other factors equal, the substitution ofa gas having a lower gamma value results in an increase in the spacingbetween the pistons at the moment ol maximum pressure for the same peakpressure The choice of a gas for pistons is also important from thestandpoint of the temperatures involved since the gamma value of the gasaffects the ultimate temperature which may be reached at the moment ofmaximum pressure. It should be noted also that since in a practical casethe temperatures between the pismns may reach a very high order,exceeding the ilash temperature of most oils, there is some danger of anexplosion resulting from the oil used to lubrcate the pistons. For thisreason it is desirable that the oil used be of the noncombustible type.By employing a gas having than that of air themaxibe controlled and forthe same peak pressure will be less than that which would occur` ifair'were used, thus reducing the danger of explosion where a combustiblelubricating material is used. For example, using a gas having a gamma of1.2 the maximum temperature obtained will be approximately one-half thatof the temperature obtained usingair (gamma 1.4) for the same peakpressure.

From the foregoing it will be apparent that in accordance with thepresent invention an impact device has been provided whereby themasnitude of the shock, the velocity of the shock, the acceleration ofthe shock and the duration of the shock may be controlled. The drivingforce Fi, of course, predetermines in large part the ilnal velocity andthis, given a mass of any given size, determines the magnitude of theshock. However, for any given final velocity, the duration of the shockand the acceleration may be varied. In general, increasing the gaspressure between the pistons increases the shock duration andconsequently lowers the acceleration. n the other hand, increasing Fi byincreasing P1. the charging pressure,

the space between the and if Pr is held the same, then the velocity andacceleration are increased. Increase in velocity of course directlyaects the magnitude oi the shock.

For ps of illustratiomthe following table is given showing the vl tionsobtained by vary ing P1 and P2 in a practical embodiment oi 'this "takenas the""period of time 'required forv the impact force to increase fromone haii its peak magnitude to peak and to return to half its peakmagnitude. V represents final velocity in feet per second.

r.' Pi o D v (1 Y Y 4i s n i 4 (2 s2 is .13.5 1o a; a vsa 4 am .4 c 4 cs1an s4 4 g ix 1g t Lx 4`4 g l J Since, as hereinbefore stated, in apractical case the mass M will exceed substantially the mass m of thepiston d8, the acceleration during the recoil of the piston 2B willproportionately exceed the maximum acceleration during the forwardmotion of the piston 28 and thus the kinetic energy of the piston 28 mayreach a very high magnitude. Consequently, unless some means is providedfor preventing a rebound of the piston 28 a secondary shock will beproduced. From a test standpoint this is highly undesirable since acomputation of the forces involved and applied to the platform duringthe secondary shock is extremely diillcult. Furthermore, since theprimary purpose of this impact device is to simulate the shock resultingfrom the ring of a ships gun, or an explosion resulting from enemyaction, either of which involve no substantial secondary shocks, it isdesirable that secondary shocks be reduced to unimportant values if noteliminated entirely from the impact device. However, because of theforces involved, it is impractical to design a latching mechanismwhereby rebound of the piston 28 may be prevented. Therefore, inaccordance with the present invention, the exhaust chamber andassoelated exhaust ports 14 are so designed that as the piston 2lrecoils, tending to compress the air in the charging chamber andtransferring the kinetic energy from the piston to potential energy inthe air, the energy delivered to the air in the charging chamber isdissipated as the air escapes through the ports 14. The size of theports 14 is selected with reference to the size of the charging chamberand the energy to be dissipated so that by the time the piston 28 hasmoved rearwardly suilicientlyto close the ports I3 leading to theexhaust chamber, substantially all of the kinetic energy in the piston28 is expended and in this manner secondary shocks substantially I0avoided.

increases the velocity (5 While most of the kinetic energy gained duringrecoil is expended compressing the air in the charging chamber and thepotential energy so accumulatedin the air is dissipated as the airescapes through the ports 14, should some energy remain, the remainingenergy compresses the air trapped in the portion of the charging chamberto the rear of the exhaust port I3 causing a slight rebound of thepiston 28. However, since, as the piston 28 recoils, it opens thechamber formed between ports i3, the pressure in the exhaust chamber isapplied to the forward face of the piston 28. This equalization of thepressure aids in reducing the possibility of a secondary shock. Inpractice it has been found that by a proper selection of the size of theports 14 the rebound, if it occurs at all, will be insufficient to causea secondary shock.

Where herein the several parts'of this invention have been referred toas being in an upper or lower position, or in a right or left position,it will be understood that this is done solely to facilitate descriptionand that the references relate only to the relative positions of theparts as shown in the accompanying drawings.

While but one embodiment of this inventio has been shown and described,it will be understood that many changes and modifications may be madetherein without departing from the spirit or scope of the presentinvention.

The invention shown and described herein may be manufactured and used byor for the Government of the United States of America for governmentalpurposes without the payment of any royalties thereon or therefor.

What is claimed is:

1. In a pneumatic impact device, a cylinder. a striker piston slidablyjournalled in the forward end thereof, a driving piston slidablyjournalled in said cylinder and spaced rearwardly from said strikerpiston, means for adjusting the initial l pressure between said pistons,means for applying pressure to said driving piston to cause said strikerpiston to deliver an impact, and an exhaust valve for said cylinderfully opened at the the pistons to thev exhaust end of the piston strokeat a given rate independently of the speed of the piston.

2. In a pneumatic impact device, a cylinder, a striker piston slidablyjournalled in the forward end thereof, a driving piston slidablyjournalled in said cylinder and spaced rearwardly from said strikerpiston, means for adjusting the initial pressure between said pistons,means for applying pressure to said driving piston to cause said strikerpiston to deliver an impact, and pneumatic means associated with saidcylinder for absorb'ing the kinetic energy resulting from the recoil ofsaid driver piston to prevent .secondary shocks.

3. In a pneumatic impact device, a cylinder, a striker piston slidablyjournalled in the forward end thereof, a driving pi'ston slidablyjournalled in said cylinder and spaced rearwardly from said strikerpiston, means for adjusting the initial pressure between said pistons,means for applying pneumatic pressure to said driving piston to causesaid striker piston to deliver an impact, and latching mechanismassociated with said driver piston for controlling the release of saidpiston.

4. In a pneumatic` impact device, a cylinder, a striker piston slidablyjournalled in the forward end thereof, a driving piston slidablyjournalled in said cylinder and spaced rearwardly from said strikerpiston, means for adjusting the initial pressure between said pistons,means for applying pressure to said saidstriker piston to deliver animpact, an exdrivlng piston to cause 14 haust chamber connected to saidcylinder, a poppet valve for opening and closing said exhaust chamber,latching means for locking said poppet` valve in closed position, and'means controlled by the movement of said driver piston for releasingsaid latching means.

5. In a pneumatic impact device, a cylinder, a striker piston-slidablyjournalled in the forward endthereof, a driving piston slidablyjournalled in said cylinder `and spaced from said striker piston, a gashaving a gamma value substantially that of argon in the space betweensaid pistons, means for applying pressure to said driving piston tocause said striker piston to deliver an impact, and an exhaust valve forsaid cylinder fully opened at the end of the piston stroke at a givenrate independently of the speed of the piston.

6. In a pneumatic impact device, a cylinder, a striker piston slidablyjournalled in the forward end thereof, a4 driving piston slidablyjournalled in said cylinder and spaced from 'said striker from therecoil of said driver piston to prevent secondary shocks.

7. In a pneumatic impact device, a cylinder, a striker piston slidablyjournalled in the forward end thereof, a shaft afxed to said piston andextending through an end of said cylinder, a driving piston slidablyjournalled in said cylinder and. spaced from said striker piston, ashaft fixed to said driving piston and extending through the oppositeend of said cylinder, the space between said driving piston and thelatter end of said cylinder forming a charging chamber, said chargingchamber having an exhaust chamber connected thereto, means for openingand closing said exhaust chamber, said opening and closing means beingcontrolled by the movement of said driver piston shaft, a gas in thespace between said pistons, means for adjusting the initial pressure ofthe gas between said pistons, and means for applying pressure to saiddriving piston said striker piston to deliver an'impact.

OSCAR C. DRESSER. OSCAR NORGORDEN. FRANCIS J. SHANAHAN. CARROLL R.SHULER.

REFERENCES CITED The following references are of record in the iile ofthis patent:

UNITED STATES PATENTS to cause

